Shift control apparatus and shift control method for a vehicular automatic transmission

ABSTRACT

A shift control apparatus for a vehicular automatic transmission provided with a fuel cut apparatus which cuts off fuel supplied to an engine when an engine speed exceeds a predetermined value during deceleration of a vehicle, and an automatic transmission in which a gearshift is achieved with a clutch-to-clutch downshift in which a hydraulic friction device to be released is released and a hydraulic friction device to be applied is applied, further includes a controller. The controller corrects, through learning control, an apply pressure of at least one of the hydraulic friction devices to be operated for the clutch-to-clutch downshift such that an amount of drop in a rotational speed of an input shaft of the automatic transmission increases when that amount of drop is less than a predetermined value during the clutch-to-clutch downshift.

INCORPORATION BY REFERENCE

The disclosures of Japanese Patent Application No. 2002-350526 filed onDec. 2, 2002, including the specification, drawings and abstract isincorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a shift control apparatus and shift controlmethod for a vehicular automatic transmission, which enables suppressionof a drop in rotational speed of an input shaft which occurs during aclutch-to-clutch downshift executed while a vehicle is decelerating.

2. Description of the Related Art

A shift control apparatus for a vehicular automatic transmission isknown which, when executing a clutch-to-clutch downshift, executes shifthydraulic pressure control so as to reduce an apply pressure of ahydraulic friction device to be released, which was applied in order toachieve a predetermined speed before the downshift, while increasing anapply pressure of a hydraulic friction device to be applied in order toachieve a predetermined speed after the downshift. According to JP(A)11-287318, for example, during the clutch-to-clutch downshift, feedbackcontrol is performed on the apply pressure of the hydraulic frictiondevice to be applied so that a transmitted torque capacity of thehydraulic friction device to be applied becomes constant, i.e., so thata rotational speed of an input shaft of the automatic transmissionincreases at a constant rate.

In the aforementioned shift control apparatus for a vehicular automatictransmission, the engine speed drops during the clutch-to-clutchdownshift when the vehicle is decelerating, and then increases againwhen the hydraulic friction device to be applied is applied. Thiscombination of a drop followed by an increase in engine speed results inshift shock or a delay in the shift time. Also, fuel efficiency may bereduced if the drop in engine speed is large enough to require that thefuel supply be restarted.

In comparison, it is conceivable to automatically suppress the drop inengine speed during the clutch-to-clutch downshift while the vehicle isdecelerating, and appropriately reduce or eliminate shift shock or adelay in shift time caused by that drop. It is also possible toappropriately reduce the adverse effect on fuel efficiency caused byfuel being supplied to the engine again due to a further drop in enginespeed. However, doing so may result in shift shock occurring when thereis little or no drop in engine speed.

SUMMARY OF THE INVENTION

In view of the foregoing problems, this invention thus provides a shiftcontrol apparatus and shift control method for a vehicular automatictransmission, which automatically suppresses a drop in engine speedduring a clutch-to-clutch downshift executed while a vehicle isdecelerating, appropriately reduces or eliminates shift shock or a delayin shift time caused by that drop in engine speed, and appropriatelysuppresses a reduction in fuel efficiency due to the fuel supply to theengine being restarted due to that drop in engine speed.

One aspect of the invention relates to a shift control apparatus for avehicular automatic transmission which includes i) a fuel cut apparatuswhich performs a fuel cut in which a supply of fuel to an engine is cutoff when an engine speed exceeds a predetermined value duringdeceleration of a vehicle, ii) an automatic transmission in which agearshift is achieved with a clutch-to-clutch downshift in which ahydraulic friction device to be released is released and a hydraulicfriction device to be applied is applied, and iii) a controller whichcorrects, through learning control, an apply pressure of at least one ofthe hydraulic friction devices to be operated for the clutch-to-clutchdownshift such that an amount of drop in a rotational speed of an inputshaft of the automatic transmission increases when that amount of dropis less than a predetermined value during the clutch-to-clutchdownshift.

Also, another aspect of the invention relates to a shift control methodfor a vehicular automatic transmission which includes a fuel cutapparatus which performs a fuel cut in which a supply of fuel to anengine is cut off when an engine speed exceeds a predetermined valueduring deceleration of a vehicle, and an automatic transmission in whicha gearshift is achieved with a clutch-to-clutch downshift in which ahydraulic friction device to be released is released and a hydraulicfriction device to be applied is applied. According to this shiftcontrol method, an apply pressure of at least one of the hydraulicfriction devices to be operated for the clutch-to-clutch downshift iscorrected through learning control such that an amount of drop in arotational speed of an input shaft of the automatic transmissionincreases when that amount of drop is less than a predetermined valueduring the clutch-to-clutch downshift.

According to the shift control apparatus and shift control method for avehicular automatic transmission as described above, the apply pressureof the at least one of the hydraulic friction devices to be operated forthe clutch-to-clutch downshift is corrected through learning controlsuch that the amount of drop in the rotational speed of the input shaftof the automatic transmission increases when the degree of overlapbetween the release of the hydraulic friction device to be released andthe application of the hydraulic friction device to be applied is largeand the amount of drop in the rotational speed of the input shaft of theautomatic transmission is less than the predetermined value during theclutch-to-clutch downshift. As a result, shift shock caused by the largedegree of overlap between the release of the hydraulic friction deviceto be released and the application of the hydraulic friction device tobe applied is able to be appropriately reduced or eliminated.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned embodiment and other embodiments, objects, features,advantages, technical and industrial significance of this invention willbe better understood by reading the following detailed description ofthe preferred embodiments of the invention, when considered inconnection with the accompanying drawings, in which:

FIG. 1 is a skeleton view illustrating a transverse-mounted vehiculardriving apparatus for an FF vehicle to which a shift control apparatusaccording to one exemplary embodiment of the invention is applied;

FIG. 2 is a clutch and brake application chart showing variousapplication and release combinations of clutches and brakes to achievespecific speeds in the automatic transmission shown in FIG. 1;

FIG. 3 is a block diagram of a control system, which shows the input andoutput to and from an ECU provided in the vehicle according to the firstexemplary embodiment shown in FIG. 1;

FIG. 4 is a view showing one example of a shift pattern of a shift levershown in FIG. 3;

FIG. 5 is a graph showing one example of the relationship between anaccelerator pedal operation amount A_(CC) and a throttle valve openingamount θ_(TH) used in throttle control performed by the ECU shown inFIG. 3;

FIG. 6 is a view showing a shift diagram (i.e., shift map) used in shiftcontrol of the automatic transmission performed by the ECU shown in FIG.3;

FIG. 7 is a diagram illustrating main portions of a hydraulic pressurecontrol circuit shown in FIG. 3;

FIG. 8 is a functional block diagram illustrating a major part of acontrol function of the ECU shown in FIG. 3, i.e., a shift controloperation of the automatic transmission;

FIG. 9 is a time chart showing a major part of the control function ofthe ECU shown in FIG. 3, i.e., a basic control operation for aclutch-to-clutch downshift of the automatic transmission;

FIG. 10 is a flowchart of a main routine for illustrating a learningcorrection routine of a time until the start of sweep control of ahydraulic friction device to be released in a major part of the controlfunction of the ECU shown in FIG. 3, i.e., in the shift controloperation of the automatic transmission during a downshift of theautomatic transmission while the vehicle is decelerating;

FIG. 11 is a flowchart of a learning correction value calculatingroutine which is a subroutine in the routine shown in FIG. 10;

FIG. 12 is a flowchart of a neutral avoidance learning routine which isa subroutine in the routine shown in FIG. 11;

FIG. 13 is a flowchart of a tie-up avoidance learning routine which is asubroutine in the routine shown in FIG. 11;

FIG. 14 is a time chart illustrating a case in which a normal learningroutine or a high speed learning routine for a neutral tendency isexecuted in a major part of the control function of the ECU shown inFIG. 3, i.e., in the shift control operation of the automatictransmission during a downshift while the vehicle is decelerating;

FIG. 15 is a time chart illustrating a case in which an emergencylearning routine for the neutral tendency is executed in a major part ofthe control function of the ECU shown in FIG. 3, i.e., in the shiftcontrol operation of the automatic transmission during a downshift whilethe vehicle is decelerating; and

FIG. 16 is a time chart illustrating a case in which an emergencylearning routine for tie-up is executed in a major part of the controlfunction of the ECU shown in FIG. 3, i.e., in the shift controloperation of the automatic transmission during a downshift while thevehicle is decelerating.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following description and the accompanying drawings, the presentinvention will be described in more detail in terms of exemplaryembodiments.

FIG. 1 is a skeleton view of a transverse-mounted vehicular drivingapparatus for a vehicle such as a FF (front engine, front drive)vehicle. Output from an engine 10, which is an internal combustionengine such as a gasoline engine, is transmitted to driven wheels (frontwheels), not shown, via power transmitting apparatuses such as a torqueconverter 12, an automatic transmission 14, and a differential gear unit16. The torque converter 12 includes a pump impeller 20 which isconnected to a crankshaft 18 of the engine 10, a turbine impeller 24which is connected to an input shaft 22 of the automatic transmission14, a stator 30 which is fixed to a housing 28, which is a non-rotatablemember, via a one-way clutch 26, and a lockup clutch 32 that directlyconnects the crankshaft 18 with the input shaft 22 via a damper, notshown. A mechanical oil pump 21 such as a gear pump is connected to thepump impeller 20. This oil pump 21 is driven together with the pumpimpeller 20 by the engine 10 so as to generate hydraulic pressure usedfor shifting and lubrication and the like. The engine 10 is a drivingpower source for running a vehicle. The torque converter 12 is a fluidcoupling which is capable of boosting torque.

The automatic transmission 14 includes a first planetary gearset 40, asecond planetary gearset 42, and a third planetary gearset 46, all ofwhich are of the single pinion type, and an output gear 48. The firstplanetary gearset 40 and second planetary gearset 42 are both providedon the same axis as the input shaft 22, with a carrier of the firstplanetary gearset 40 coupled to a ring gear of the second planetarygearset 42 and a carrier of the second planetary gearset 42 coupled to aring gear of the first planetary gearset 40, such that the firstplanetary gearset 40 and second planetary gearset 42 together form acarrier-ring, carrier-ring (CR—CR) coupled planetary gearset. The thirdplanetary gearset 46 is provided on the same axis as a countershaft 44which is parallel with the input shaft 22. The output gear 48 is fixedto one end of the countershaft 44 and is meshed with the differentialgear unit 16. The structural elements of the first planetary gearset 40,the second planetary gearset 42, and the third planetary gearset 46,i.e., a sun gear, a ring gear, and a carrier that rotatably supportsplanet gears that mesh with the sun gear and ring gear, can either beselectively coupled together by four clutches C0, C1, C2, and C3, orselectively coupled to the housing 28, which is a non-rotatable member,by three brakes B1, B2, and B3. Further, two one-way clutches F1 and F2enable a carrier K2 and a sun gear S3, respectively, to either rotate ina given direction with respect to the housing 28, or engage with thehousing 28. Because the differential gear unit 16 is symmetrical withrespect to the axis of the drive axles, the bottom half thereof will beomitted.

The set of the first planetary gearset 40 and second planetary gearset42 on the same axis as the input shaft 22, together with the clutchesC0, C1, C2, the brakes B1 and B2, and the one-way clutch F1 make up aprimary transmitting portion MG capable of four forward speeds and onereverse speed. The third planetary gearset 46 on the same axis as thecountershaft 44, together with the clutch C3, the brake B3, and theone-way clutch F2 make up a secondary transmitting portion, i.e., anunder drive portion U/D. In the primary transmitting portion MG, theinput shaft 22 is coupled to i) the carrier K2 of the second planetarygearset 42 via the clutch C0, ii) a sun gear S1 of the first planetarygearset 40 via the clutch C1, and iii) a sun gear S2 of the secondplanetary gearset 42 via the clutch C2. A ring gear R1 of the firstplanetary gearset 40 is connected to the carrier K2 of the secondplanetary gearset 42, and a ring gear R2 of the second planetary gearset42 is connected to a carrier K1 of the first planetary gearset 40. Thesun gear S2 of the second planetary gearset 42 is coupled to the housing28 via the brake B1. The ring gear R1 of the first planetary gearset 40is coupled to the housing 28 via the brake B2. The one-way clutch F1 isprovided between the carrier K2 of the second planetary gearset 42 andthe housing 28. A first counter gear G1, which is fixed to the carrierK1 of the first planetary gearset 40, is in mesh with a second countergear G2, which is fixed to a ring gear R3 of the third planetary gearset46. In the underdrive portion U/D, a carrier K3 and the sun gear S3 ofthe third planetary gearset 46 are coupled together via the clutch C3.Also in the underdrive portion U/D, the brake B3 and the one-way clutchF2 are provided in parallel between the sun gear S3 and the housing 28.

The clutches C0, C1, C2, and C3 and the brakes B1, B2, B3 (hereinaftersimply referred to as “clutches C” and brakes B”, respectively, when notspecified further) are hydraulic friction devices, the clutches C being,for example, multi-disc clutches and the brakes B being multi-discclutches or band brakes or the like which are applied by hydraulicactuators. These clutches C and brakes B are switched between an appliedstate and a released state, as shown in FIG. 2, for example, byswitching solenoids S1 to S5 and linear solenoid valves SL1, SL2, andSLU of a hydraulic pressure control circuit 98 (see FIG. 3) between anenergized state and a de-energized state, or by switching a hydrauliccircuit using a manual valve, not shown. Each speed, i.e., five forwardspeeds, one reverse speed, and a neutral speed, is achieved according toa position of a shift lever 72 (see FIG. 3). The denotations “1st” to“5th” in FIG. 2 denote the first forward speed to the fifth forwardspeed, respectively. A single circle indicates an applied state of theclutches C and brakes B. An “X” indicates a released state of theclutches C and brakes B. A triangle indicates an applied state of theclutches C and brakes B only during driving. The shift lever 72 isoperated in a shift pattern which includes a park position “P”, areverse drive position “R”, a neutral position “N”, and forward drivepositions “D”, “4”, “3”, “2”, and “L”, as shown in FIG. 4, for example.When the shift lever 72 is in the “P” or the “N” position, thetransmission is in a neutral speed, i.e., a non-driving speed in whichthe transmission of power to the wheels is interrupted. When the shiftlever 72 is in the “P” position, the driven wheels are mechanicallyprevented from rotating by a mechanical parking mechanism, not shown.Also, the five forward speeds and the one reverse speed achieved whenthe shift lever 72 is in any one of the forward drive positions, such asthe “D” position, or the “R” position, respectively, correspond todriving speeds. Further, as shown in FIG. 2, a shift between secondspeed and third speed is a clutch-to-clutch or synchronous shift, inwhich the clutch C0 is applied at substantially the, same time the brakeB1 is released, or vice versa. Similarly, a shift between third speedand fourth speed is a clutch-to-clutch shift in which the clutch C1 isapplied at substantially the same time the brake B1 is released, or viceversa. In the above-mentioned hydraulic friction device, a line pressureregulated by a turbine torque T_(T), i.e., an input torque T_(IN) of theautomatic transmission 14, or a throttle opening amount θ_(TH) which isa value representative of the input torque T_(IN), is used as the basepressure for the hydraulic friction devices.

FIG. 3 is a block diagram illustrating a control system provided in avehicle, which controls the engine 10 and automatic transmission 14 andthe like shown in FIG. 1. According to this control system, theoperation amount (accelerator opening amount) A_(CC) of an acceleratorpedal 50 is detected by an accelerator operation amount sensor 51. Thisaccelerator pedal 50 corresponds to an accelerator operating member andcan be depressed to a large degree depending on the amount of outputrequired by a driver. The accelerator pedal operation amount A_(CC)corresponds to the amount of required output. An electronic throttlevalve 56 is provided in an intake pipe of the engine 10. A throttleactuator 54 changes the opening amount of this electronic throttle valve56 so that it has an opening angle (opening amount) θ_(TH) (%)determined based on the accelerator. pedal operation amount A_(CC) froma pre-stored (i.e., preset) relationship shown in FIG. 5. Thisrelationship is set such that the throttle opening amount θ_(TH)increases as the accelerator pedal operation amount A_(CC) becomeslarger. Also, in a bypass passage 52 which bypasses the electronicthrottle valve 56 is provided an ISC (idle speed control) valve 53 thatcontrols the intake air quantity when the electronic throttle valve 56is fully closed in order to control an idle speed N_(EIDL) of the engine10.

In addition, other sensors and switches are also provided, such as anengine speed sensor 58 for detecting an engine speed N_(E) of the engine10, an intake air quantity sensor 60 for detecting an intake airquantity Q of the engine 10, an intake air temperature sensor 62 fordetecting a temperature T_(A) of the intake air, a throttle sensor 64with an idle switch for detecting when the electronic throttle valve 56is fully closed (i.e., when the engine 10 is in an idle state) as wellas for detecting the opening amount θ_(TH) of that electronic throttlevalve 56, a vehicle speed sensor 66 for detecting a rotational speedN_(OUT) of the countershaft 44 which corresponds to the vehicle speed V,a coolant temperature sensor 68 for detecting a coolant temperatureT_(W) of the engine 10, and a brake switch 70 for detecting whether afoot brake is being operated. In addition, other sensors and switchesprovided include a lever position sensor 74 for detecting a leverposition (i.e., an operating position) P_(SH) of the shift lever 72, aturbine rotational speed sensor 76 for detecting a turbine rotationalspeed N_(T) (=rotational speed N_(IN) of the input shaft 22), an ATfluid sensor 78 for detecting an AT fluid temperature T_(OIL), which isthe temperature of the hydraulic fluid within the hydraulic pressurecontrol circuit 98, a counter rotational speed sensor 80 for detecting arotational speed N_(C) of the first counter gear G1, an ignition switch82, and a knock sensor 84. Signals from these sensors indicative of theengine speed N_(E), intake air quantity Q, intake air temperature T_(A),throttle valve opening amount θ_(TH), vehicle speed V, engine coolanttemperature T_(W), a brake operation, lever position P_(SH) of the shiftlever 72, turbine rotation speed N_(T), AT fluid temperature T_(OIL),counter rotational speed N_(C), the operational position of the ignitionswitch 82, and knocking of the engine 10 and the like are supplied to anelectronic control unit (ECU) 90. The brake switch 70 is an ON-OFFswitch that switches the brake on or off depending on whether the brakepedal, which operates a main brake, is depressed or not.

The ECU 90 includes a microcomputer that has a CPU, RAM, ROM, aninput/output interface and the like. The CPU controls the output of theengine 10 and the shifting of the automatic transmission 14 and the likeby processing signals according to a program stored in the ROMbeforehand while using the temporary storage function of the RAM. Whennecessary, the CPU may be configured such that a portion thereof forengine control is separate from a portion thereof for shift control. Theoutput of the engine 10 is controlled by controlling the electronicthrottle valve 56 open and closed with the throttle actuator 54,controlling a fuel injection valve 92 in order to control the fuelinjection quantity, controlling an ignition device 94, such as anigniter, in order to control the ignition timing, and controlling theISC valve 53 in order to control the idle speed. The electronic throttlevalve 56 is controlled by, for example, driving the throttle actuator 54based on the actual accelerator pedal operation amount A_(CC) accordingto the relationship between the accelerator pedal operation amountA_(CC) and the throttle valve opening amount θ_(TH), shown in FIG. 5 forexample, and increasing the throttle valve opening amount θ_(TH) as theaccelerator pedal operation amount A_(CC) increases. When the engine 10is started, the crankshaft 18 is cranked by a starter (i.e., an electricmotor) 96. Further, in the shift control of the automatic transmission14, the CPU 90 first determines the speed that the automatictransmission 14 should shift into from the current speed based on theactual throttle valve opening amount θ_(TH) and the vehicle speed Vaccording to a pre-stored shift diagram (i.e., shift map), shown in FIG.6, for example. The CPU 90 then outputs a shift command for starting ashift operation to shift the automatic transmission 14 from the currentspeed to the determined speed. The ECU 90 also switches solenoids S4 andSR of the hydraulic pressure control circuit 98 on (energized) and off(de-energized) and continually changes the energized state of the linearsolenoid valves SL1, SL2, and SL3 and the like of the hydraulic pressurecontrol circuit 98 by duty control or the like, so that shift shock dueto a change in driving force or the like will not occur and thedurability of the friction members will not reduced. In FIG. 6, thesolid lines are upshift lines and the broken lines are downshift lines.The automatic transmission 14 shifts into a speed on the low speed sidehaving a large gear ratio (=input rotational speed N_(IN)/outputrotational speed N_(OUT)) as the vehicle speed V decreases or thethrottle valve opening amount θ_(TH) increases. Denotations “1” through“5” in the drawing refer to the first speed “1st” through the fifthspeed “5th”.

FIG. 7 is a functional block diagram illustrating main portions of thehydraulic pressure control circuit 98 that are related to a 3→2downshift. The hydraulic fluid pressure-fed from the hydraulic pump 88is regulated by a first regulator valve 100, which is a relief valve, soas to become a first line hydraulic pressure P_(L1). The hydraulic fluidflowing out through the first regulator valve 100 is then regulated by asecond regulator valve 102, which is also a relief valve, so as tobecome a second line hydraulic pressure P_(L2). The first line hydraulicpressure P_(L1) is supplied via a hydraulic line L1 to a manual valve104 which is connected to the shift lever 72. When the shift lever 72 isshifted into either the D position (i.e., range) or the S position(i.e., range), a forward position pressure P_(D) which is equal to thefirst line hydraulic pressure P_(L1) is supplied from the manual valve104 to each solenoid valve SL1, SL2, SL3, and the like, as well as to ashift valve, not shown. FIG. 7 shows the clutch C0 which is released toachieve the 3→2 downshift, the brake B1 which is applied to achieve the3→2 downshift, the linear solenoid valve SL3 used to directly controlthe apply pressure P_(B1) of the brake B1, the linear solenoid valve SL2used to directly control the apply pressure P_(C0) of the clutch C0, ahydraulic pressure sensor 106 connected to the brake B1 for detectingthe apply pressure P_(B1), a hydraulic pressure sensor 108 connected tothe clutch C0 for detecting the apply pressure P_(C0), a B1 clutchcontrol valve 110 for regulating the apply pressure P_(B1) while thehydraulic fluid is being supplied, a C0 clutch control valve 112 forregulating the apply pressure P_(C0) while the hydraulic fluid is beingsupplied, a B1 accumulator 114 for reducing an increase in the applypressure P_(B1) of the brake B1, and a C0 accumulator 116 for reducingan increase in the apply pressure P_(C0) of the clutch C0.

FIG. 8 is a functional block diagram illustrating a major part of acontrol function of the ECU 90, i.e., a shift control operation of theautomatic transmission 14. FIG. 9 is a time chart illustrating a basiccontrol operation for a clutch-to-clutch downshift of the automatictransmission 14. The state of the vehicle during this basic controloperation is one in which a fuel cut operation (i.e., fuel supply to theengine 10 is cut off) by the fuel cut apparatus 118 that is executedwhen the engine speed N_(E) is greater than a preset fuel cut lowerlimit speed (i.e., a fuel cut cancellation value C_(F)) when theaccelerator pedal is not being depressed and the vehicle isdecelerating, is in effect, such as when a clutch-to-clutch downshiftcontrol operation such as a 3→2 downshift is being performed, forexample. Referring back to FIG. 8, rotational speed detecting means 120detects the turbine rotational speed N_(T) (=rotational speed N_(IN) ofthe input shaft 22) from a signal from the turbine rotational speedsensor 76, for example, and also detects the engine speed N_(E) of theengine 10 from a signal from the engine speed sensor 58, for example.Inertia start determination means 130 determines (at time t₁) whetherthe turbine rotational speed N_(T) has started to increase following theshift to a low speed (e.g., second speed) during the downshift controloperation while the vehicle is decelerating.

Shift state determining means 122 determines (at time t₀) whether ashift (i.e., hydraulic pressure control) of the automatic transmission14 has started based on a signal output from the shift hydraulicpressure controlling means 124, which will be described later. The shiftstate determining means 122 then determines (at time t₂) whether theshift is complete based on whether or not the turbine rotational speedN_(T) substantially matches a rotational speed γ2×N_(OUT) calculatedfrom the rotational speed N_(OUT) of the countershaft 44 detected by thevehicle speed sensor 66 and the gear ratio γ2 of the speed (e.g., secondspeed) after the shift is complete. The shift state determining means122 then determines (at time t₃) whether the shift hydraulic pressurecontrol performed by the shift hydraulic pressure controlling means 124has ended based on whether the apply pressure P_(B1) detected by thehydraulic pressure sensor 106 which is connected to the brake B1 hasreached the maximum value such that the brake B1 is fully applied. Also,fuel cut controlling means 126 determines whether it is necessary tosupply fuel to the engine 10 based on the engine speed N_(E) and theaccelerator pedal operation amount A_(CC) and the like, and outputs acommand to the fuel cut apparatus 118 to cut off the supply of fuel tothe engine 10 depending on that determination. For example, when thevehicle is decelerating, during which the accelerator pedal operationamount A_(CC) is zero, but the engine speed N_(E) of the engine 10 isnot below a predetermined value (i.e., a fuel cut cancellation valueC_(F)), a fuel cut command is output so that a fuel cut is performed.When the engine speed N_(E) of the engine 10 slows to the predeterminedvalue, the fuel cut command stops being output so that the fuel cut isstopped, i.e., the fuel cut is cancelled. Fuel cut state determiningmeans 128 determines whether the fuel cut has been cancelled based on asignal output to the fuel cut controlling means 126.

When the speed into which the automatic transmission 14 should beshifted from the current speed is determined based on the actualthrottle valve opening θ_(TH) and the vehicle speed V from the shiftdiagram (i.e., the shift map) shown in FIG. 6, which is storedbeforehand, for example, the shift hydraulic pressure controlling means124 outputs a signal to the hydraulic pressure control circuit 98 tochange the apply pressure of the hydraulic friction device so as toswitch the automatic transmission 14 from the current speed to the otherspeed. For example, during the 3→2 clutch-to-clutch downshift as shownin FIG. 9, an apply driving signal S_(PB1) is output to the linearsolenoid valve SL3 which directly controls the apply pressure P_(B1) ofthe brake B1, which is a hydraulic friction device to be applied, and arelease driving signal S_(PC0) is output to the linear solenoid valveSL2 which directly controls the apply pressure P_(C0) of the clutch C0,which is a hydraulic friction device to be released. The apply drivingsignal S_(PB1) will now be described. First, a signal S_(PB1W) is outputto keep the apply pressure P_(B1) at a constant predetermined applypressure P_(B1W) which is set lower than the pressure at which the brakeB1 starts to be applied during the time t_(B1W) from the shift startingpoint t₀. After the apply pressure P_(B1) is kept at the constantpressure, a signal is then output to smoothly increase it at a presetconstant rate until it has been determined by the inertia startdetermining means 130 that inertia has started (time t₁). Next, a signalto smoothly change the apply pressure P_(B1) is output for feedbackcontrol so that the rotational speed N_(IN) of the input shaft (i.e.,the turbine rotational speed N_(T)) smoothly increases at apredetermined constant rate from time t₁ until it has been determined bythe shift state determining means 122 that the shift is complete (timet₂). A signal is then output to rapidly increase the apply pressureP_(B1) from time t₂ so as to fully apply the brake B1 (time t₃). Here,during time t_(B1A) from the start of the shift, a signal that is largerthan the signal S_(PB1W) is output to quickly increase the applypressure P_(B1) to the predetermined apply pressure P_(B1W) during timet_(B1W).

Next, the release driving signal S_(PC0) will be described. First, asignal S_(PC0W) is output for keeping the apply pressure P_(C0) at aconstant predetermined apply pressure (i.e., a holding pressure) P_(C0W)during time t_(C0W). This predetermined apply pressure P_(C0W) is setlower than the maximum apply pressure, which is the first line hydraulicpressure P_(L1), i.e., the base pressure before the start of the shiftor the originally supplied hydraulic pressure, and slightly higher thanthe pressure at which the clutch C0 starts to be released. After theapply pressure P_(C0) is kept at the constant pressure, a signal is thenoutput to smoothly decrease (hereinafter, this smooth decrease is alsoreferred to as “sweep”) it at a constant rate so as to fully release theclutch C0. Here, during time t_(C0A) after the start of the shift, asignal to fully release the clutch C0 is output to quickly decrease theapply pressure P_(C0) to the predetermined apply pressure P_(C0W) duringtime t_(C0W) after the start of the shift. The time t_(C0W) is a holdingtime for the holding pressure, during which the apply pressure P_(C0) ismaintained at the constant predetermined pressure P_(C0W). Because thetime t_(C0W) is also the time from the start of the shift until theapply pressure P_(C0) starts to be smoothly changed (decreased), i.e.,because the time t_(C0W) is also the time from the start of the shiftuntil the apply pressure P_(C0) starts to be gradually decreased (i.e.,until the start of sweep), time t_(C0W) also denotes the time until thestart of sweep control (i.e., the time before starting to decrease thepressure).

Accordingly, when there is only a small degree of overlap between theapplication of the clutch C0 and the application of the brake B1, forexample, when the time until the start of sweep control t_(C0W) isshort, when, during the 3→2 clutch-to-clutch downshift while the vehicleis decelerating, the shift hydraulic pressure controlling means 124decreases the apply pressure P_(C0) of the clutch C0, which is thehydraulic friction device to be released, while simultaneouslyincreasing the apply pressure P_(B1) of the brake B1, which is thehydraulic friction device to be applied, there is a tendency for drivingwheels (not shown) and the input shaft 22 become in a disconnectedstate, i.e., a neutral state, (hereafter referred to as “neutraltendency”) resulting in a momentary drop in both the turbine rotationalspeed N_(T) and the engine speed N_(E) (hereinafter referred to as“undershooting”; see FIG. 14). As a result, shift shock (a phenomenonresembling momentary engine brake) may occur when the engine speed N_(E)increases due to application of the brake B1 and the shift time mayincrease. Further, if the neutral tendency continues, the amount ofundershooting of the engine speed N_(E) may increase to the extent thatthe fuel cut operation by the fuel cut controlling means 126 iscancelled, which may reduce the improvement in fuel efficiency achievedby the fuel cut. In contrast, when there is a large degree of overlapbetween the application of the clutch C0 and the application of thebrake B1, for example, when the time until the start of sweep controlt_(C0W) is long, the automatic transmission 14 may temporarily lock upand become in a tie-up state in which the torque of the output shaft ofthe automatic transmission 14 suddenly decreases temporarily, resultingin shift shock and leading to degradation of the hydraulic frictiondevices of the automatic transmission 14. In this exemplary embodiment,the time until the start of sweep control t_(C0W) is sequentiallychanged to the optimum value according to a repeated learning correctionroutine so that the neutral tendency and tie-up will not occur.

In this exemplary embodiment, lockup clutch slip controlling means, notshown, is also provided which outputs a driving signal S_(SLU) for thesolenoid valve SLU that controls an apply pressure P_(LU) of the lockupclutch 32 in order to control a rotational speed difference N_(SLP)(=N_(E)−N_(T)) between the turbine rotational speed N_(T) and the enginespeed N_(E) to a target rotational speed difference N_(SLP)*. From timet₀ to time t₁, the turbine rotational speed N_(T) and engine speed N_(E)gradually decrease as the vehicle decelerates, with the rotational speeddifference N_(SLP) being made to substantially match the targetrotational speed difference N_(SLP)*, e.g., −50 rpm, by the drivingsignal S_(SLU) for the solenoid value SLU. From time t₁ to time t₂, theturbine rotational speed N_(T) starts to increase as the brake B1 isapplied. The rate of this increase is controlled so as to besubstantially constant by feedback control with the apply pressureP_(B1) of the brake B1. At this time, the driving signal S_(SLU) for thesolenoid valve SLU is constant so the engine speed N_(E) increases alongwith the turbine rotational speed N_(T), but for a slightly longer time.Further, from time t₂ to time t₃, the turbine rotational speed N_(T)changes to a speed corresponding to the vehicle speed as the shift ends,and the rotational speed difference N_(SLP) is again made tosubstantially match the target rotational speed difference N_(SLP)*,e.g., −50 rpm, by feedback control using the driving signal S_(SLU) forthe solenoid valve SLU.

In the downshift control operation (see FIG. 14), undershooting amountcalculating means 132 calculates an undershooting amount N_(US) of theturbine rotational speed N_(T) generated when there is little overlapbetween the application of the clutch C0 and the application of thebrake B1, i.e., when the neutral tendency exists, according to thedifference (i.e., N_(US)=N_(TP)−N_(T)) between an estimated turbinerotational speed N_(TP) (=γ₃×N_(OUT)) derived from the rotational outputN_(OUT) of the countershaft 44 and the gear ratio γ₃ of the speed beforethe shift (e.g., third speed), and the actual turbine rotational speedN_(T). A maximum undershooting amount N_(USMAX) is then obtained byconsecutive comparisons with the size of this undershooting amountN_(US). More specifically, the maximum undershooting amount N_(USMAX) iscalculated by first initializing (i.e., resetting) the value thereof tozero and then comparing the sizes of the maximum undershooting amountN_(USMAX) and the undershooting amount N_(US). If the undershootingamount N_(US) is larger, that value replaces the maximum undershootingamount N_(USMAX). The subsequent maximum undershooting amount N_(USMAX)and the undershooting amount N_(US) are compared again and the largervalue is used as the maximum undershooting amount N_(USMAX). Thenundershooting amount determining means 134 determines whether the actualmaximum undershooting amount N_(USMAX) is equal to, or greater than, atarget undershooting amount N_(USU), which is a first predeterminedvalue, based on shift shock and the shift time and the like, or whetherthe actual maximum undershooting amount N_(USMAX) is equal to, or lessthan, an allowable undershooting amount N_(USD), which is a secondpredetermined value lower than the first predetermined value, based onshift shock and the shift time and the like. The target undershootingamount N_(USU) is a so-called upper limit value for the region of themaximum undershooting amount N_(USMAX) which is to be the target. If theactual maximum undershooting amount N_(USMAX) exceeds this value, theneutral tendency increases. Also, the allowable undershooting amountN_(USD) is a so-called lower limit value for the region of the maximumundershooting amount N_(USMAX) which is to be the target. If the actualmaximum undershooting amount N_(USMAX) falls below this value, there isa tendency for tie-up to occur.

Learning allowance determining means 136 determines whether a conditionto start a learning correction routine is fulfilled in the learningcorrection routine at the time until the start of sweep control t_(C0W).For example, the learning allowance determining means 136 determineswhether the AT fuel temperature T_(OIL) and the coolant temperatureT_(W) of the engine 10 and the like are stable, whether the varioussensors, such as the AT fluid temperature sensor 78 and the coolanttemperature sensor 68, or the turbine rotational speed sensor 76 and thelike, are operating normally, and whether the shift is a single shiftsuch as a 3→2 downshift. Memory state determining means 138 determineswhether the learning correction routine was executed when EPROM such asEEPROM (electrically erasable programmable read-only memory) in which isstored, for example, a learning correction value L for the time untilthe start of sweep control t_(C0W), was in its initial state, or afterits memory was initialized (i.e., cleared). The initial state of theEEPROM is that of when it is either initially installed or replaced inthe vehicle and the learning correction routine has not yet beenperformed.

Learning number updating means 140 updates a learning number n by adding1 to the last learning number n stored in the EEPROM when the learningcorrection routine is executed during the time until the start of sweepcontrol t_(C0W), for example, and then stores that updated learningnumber n. Also, in the first learning correction routine when the EEPROMis in the initial state or after its memory has been initialized (i.e.,cleared), the learning number n is updated so that n=0 and that updatedlearning number n is then stored in memory. Learning number determiningmeans 142 determines whether the normal learning routine may be executedby determining, for example, whether the learning number n of thelearning correction routine for the time until the start of sweepcontrol t_(C0W) exceeds a predetermined number n_(C). This is because,although the time until the start of sweep control t_(C0W) isconsecutively changed to the optimal value by repeating the learningcorrection routine, when the learning number n is small, dispersion inthe maximum undershooting amount N_(USMAX) due to deviation amongvehicles is unavoidable, so a learning correction routine different fromthe normal learning correction routine that is performed when thelearning number n is large, for example, changing the coefficient to bemultiplied by the maximum undershooting amount N_(USMAX), is necessaryin order to quickly reflect the learning correction value L in the nextshift control operation. The predetermined number n_(C) is therefore setto 2 to 5, for example.

Learning controlling means 144 is provided with learning correctionvalue calculating means 146 and sweep start time calculating means 148.The learning controlling means 144 sequentially changes the time untilthe start of sweep control t_(C0W) of the release driving signal S_(PC0)output to the linear solenoid valve SL2 that directly controls the applypressure P_(C0) of the clutch C0, which is the hydraulic friction deviceto be released, to the optimal value by repeating the learningcorrection routine so that the turbine rotational speed N_(T) will notdrop and tie-up will not occur. This learning controlling means 144prevents the turbine rotational speed N_(T) from dropping and tie-upfrom occurring by keeping the apply driving signal S_(PB1) output to thelinear solenoid valve SL3 that directly controls the apply pressureP_(B1) of the brake B1, which is the hydraulic friction device to beapplied, constant each time and executing the learning control routineonly for the time until the start of sweep control t_(C0W) of therelease driving signal S_(PC0).

When it is determined by the undershooting amount determining means 134that the drop in the turbine rotational speed N_(T) is large, thelearning correction value calculating means 146 calculates the learningcorrection value L according to the fuel cut state determined by thefuel cut state determining means 128 in order to avoid the neutraltendency. If the fuel cut is still in effect, a new learning correctionvalue L_(NCUT) (=L_(C)+G×N_(USMAX)) is obtained by adding the product ofthe maximum undershooting amount N_(USMAX) and a coefficient G (gain) tothe current learning correction value L_(C). The gain G is a valuedetermined beforehand in order to reflect the maximum undershootingamount N_(USMAX) in the new learning correction value L_(NCUT). The gainG becomes a normal learning gain G_(F) if the learning number n exceedsthe predetermined number n_(c), and becomes a high speed learning gainG_(K) if the learning number does not exceed the predetermined numbern_(C). The high speed learning gain G_(K) is a value larger than thenormal learning gain G_(F) so that the learning correction value L isquickly reflected in the next shift control operation. Also, because thetime until the start of sweep control t_(C0W) when the fuel cut has beencancelled is shorter than it is during normal learning, the applypressure P_(C0) of the clutch C0, which is the hydraulic friction deviceto be released, is quickly reduced so the neutral tendency exists forlonger and an undershooting amount N_(EUS) of the engine speed N_(E)becomes larger. Accordingly, for the purpose of improving fuelefficiency and the like as well, it is necessary to make theundershooting amount N_(EUS) an amount in which the fuel cut will not becancelled in the fewest number of times possible. Therefore, instead ofcalculating using the normal learning, a new learning correction valueL_(NCAN) (=L_(C)+L_(NE)) is obtained by adding a learning correctionvalue for emergency neutral avoidance learning L_(NE) to the currentlearning correction value L_(C). The value of the maximum undershootingamount N_(USMAX) calculated from the undershooting amount N_(US) willnot be a correct maximum value because the fuel cut has been cancelledand the engine speed N_(E) has increased. Therefore, a predeterminedvalue, not the product of the maximum undershooting amount N_(USMAX) andthe gain G used during normal learning and the like, is used as thevalue of the learning correction value for emergency neutral avoidancelearning L_(NE).

When the undershooting amount determining means 134 determines thatthere is a tie-up tendency, as well as determines whether the maximumundershooting amount N_(USMAX) is equal to, or less than, a preset zerodetermination value in which factors such as noise from, and theprecision of, the apparatus have been appropriately considered, i.e.,determines whether the maximum undershooting amount N_(USMAX) is a smallvalue substantially equal to zero, the learning correction valuecalculating means 146 calculates the learning correction value L inorder to avoid tie-up. When the maximum undershooting amount N_(USMAX)is not equal to, or less than, the zero determination value, theundershooting amount N_(US) or N_(EUS) of the turbine rotational speedN_(T) or the engine speed N_(E) are generated to some extent, but thestate of the automatic transmission 14 is close to tie-up so a newlearning correction value L_(TU) (=L_(C)−L_(TF)) is obtained bysubtracting a learning correction value for normal learning L_(TF) fromthe current learning correction value L_(C) so as to shorten the timeuntil the start of sweep control t_(C0W) in order to quickly reduce theapply pressure P_(C0) of the clutch C0, which is the hydraulic frictiondevice to be released. When the maximum undershooting amount N_(USMAX)is equal to, or less than, the zero determination value, the automatictransmission 14 is in the tie-up state so a new learning correctionvalue L_(TT) (=L_(C)−L_(TE)) is obtained by subtracting a learningcorrection value for emergency tie-up avoidance learning L_(TE) from thecurrent learning correction value L_(C) so that the time until the startof sweep control t_(C0W) becomes shorter than that for normal learningwith one execution of the learning correction routine in order toquickly avoid shift shock. A predetermined value is used for thelearning correction value for normal learning L_(TF) or the learningcorrection value for emergency tie-up avoidance learning L_(TE).

The sweep start time calculating means 148 calculates a next time untilthe start of sweep control t_(C0NEXT) (=t_(C0C)+L_(NEW)) of the applypressure P_(C0) of the clutch C0 by adding a new learning correctionvalue L_(NEW) (L_(NCUT), L_(NCAN), L_(TU) or L_(TT)) obtained by thelearning correction value calculating means 146 to the current timeuntil the start of sweep control t_(C0C). The new learning correctionvalue L_(NEW) is calculated by the learning correction value calculatingmeans 146 such that L_(NCAN)>L_(NCUT)>0 in order to increase the currenttime until the start of sweep control t_(C0C) when there is a neutraltendency, and such that L_(TT)<L_(TU)<0 in order to reduce the currenttime until the start of sweep control t_(C0C) when there is a tie-uptendency.

FIG. 10 is a flowchart illustrating a main routine for explaining thelearning correction routine of the time until the start of sweep controlt_(C0W) of the release driving signal S_(PC0) output to the linearsolenoid valve SL2 which directly controls the apply pressure P_(C0) ofthe clutch C0, which is the hydraulic friction device to be released, ina major part of the control operation of the ECU 90, i.e., in the shiftcontrol operation of the automatic transmission 14 during aclutch-to-clutch downshift while decelerating. FIG. 11 is a flowchart ofa learning correction value calculating routine which is a subroutine inthe routine shown in FIG. 10. FIG. 12 is a flowchart of a neutralavoidance learning routine which is a subroutine in the routine shown inFIG. 11. FIG. 13 is a flowchart of a tie-up avoidance learning routinewhich is a subroutine in the routine shown in FIG. 11.

Referring to FIG. 10, steps S1 and S2 correspond to the memory statedetermining means 138. In step S1 it is determined whether EPROM, suchas EEPROM (electrically erasable programmable read-only memory), inwhich is stored the learning correction value L and the like, has justbeen installed in the vehicle and is in a state in which the learningcorrection routine has not yet been executed, or whether EEPROM whichhas just been replaced is in a state in which the learning correctionroutine has not yet been executed. In step S2, it is determined whetherthe learning correction routine has been executed after the EEPROM hasbeen initialized (i.e., cleared). If the determination in step S1 orstep S2 is YES, the process proceeds on to step S3, which corresponds tothe learning number updating means 140, in which the learning number nis updated so that n=0, and that value is stored in the EEPROM. If thedetermination in both steps S1 and S2 is NO, step S3 is not executed andthe value of the learning number n stored in the EEPROM is maintained.

Next, in step S4, which corresponds to the shift state determining means122, it is determined whether the shift (i.e., hydraulic pressurecontrol) of the automatic transmission 14 has started. If thedetermination in step S4 is NO, the routine ends. If the determinationis YES, however, the value of the maximum undershooting amount N_(USMAX)is set to N_(USMAX)=0 in step S5, which corresponds to the undershootingamount calculating means 132. Steps S6 and S7 both correspond to theundershooting amount calculating means 132. In step S6, first, thecurrent undershooting amount N_(USC) is derived from the difference(N_(US)=N_(TP)−N_(T)) between the rotational speed γ₃×N_(OUT) (i.e., theestimated turbine rotational speed N_(TP)) calculated from therotational speed N_(OUT) of the countershaft 44 and the gear ratio γ₃ ofthe speed before the shift (e.g., third speed), and the actual turbinerotational speed N_(T). Then, it is determined whether the currentundershooting amount N_(USC) is greater than the maximum undershootingamount N_(USMAX). If the determination in step S6 is YES, then in stepS7 the current undershooting amount N_(USC) is made the maximumundershooting amount N_(USMAX) and the memory of the maximumundershooting amount N_(USMAX) is updated.

Next, in step S8, which corresponds to the inertia start determiningmeans 130, it is determined whether the turbine rotational speed N_(T)has started to increase. Step S6 is repeatedly executed until thedetermination in step S8 is YES. Only when the determination in step S6is YES is the current undershooting amount N_(USC) made the maximumundershooting amount N_(USMAX) and the memory of the maximumundershooting amount N_(USMAX) sequentially updated in step S7. That is,in steps S5 to S8, even if the value of the maximum undershooting amountN_(USMAX) is determined and the automatic transmission 14 is in a tie-upstate in which undershooting will not occur, the maximum undershootingamount N_(USMAX) is determined so as to equal 0. If the determination instep S8 is YES, it is determined in step S9, which corresponds to theshift state determining means 122, whether the apply pressure P_(B1)detected by the hydraulic pressure sensor 106 that is connected to thebrake B1, which is the hydraulic friction device to be applied, hasreached the maximum value so that the brake B1 is fully applied, and theshift hydraulic pressure control has ended. Step S9 is repeatedlyexecuted until the determination is YES, i.e., until the shift hydraulicpressure control has ended.

Next, in steps SG1 to SG7 in FIG. 11, which correspond to step S10 inFIG. 10, the new learning correction value L_(NEW) (L_(NCUT), L_(NCAN),L_(TU) or L_(TT)) to be added to the current time until the start ofsweep control t_(C0C) (t_(C0C0T), t_(C0CAN) or t_(C0T)) of the clutchC0, which is the hydraulic friction device to be released, is obtainedand the next time until the start of sweep control t_(C0NEXT) (t_(C0NG),t_(C0NE) or t_(C0NT),=t_(C0C)+L_(NEW)) of the apply pressure P_(C0) ofthe clutch C0 is calculated. In step SG1, which corresponds to thelearning allowance determining means 136, it is determined whether acondition to start the learning correction routine has been fulfilled.That determination is made based, for example, on whether the AT fueltemperature T_(OIL) and the coolant temperature T_(W) of the engine 10and the like are stable, whether various sensors such as the AT fluidtemperature sensor 78 and the coolant temperature sensor 68, or theturbine rotational speed sensor 76 and the like, are operating normally,and whether the shift is a single shift such as a 3→2 downshift. If thedetermination in step SG1 is NO, the routine ends.

If the determination in step SG1 is YES, then it is determined in stepSG2, which corresponds to the undershooting amount determining means134, whether the maximum undershooting amount N_(USMAX) determined insteps S5 to S8 is equal to, or greater than, the target undershootingamount N_(USU). If the determination in step SG2 is NO, it is determinedin step SG3, which also corresponds to the undershooting amountdetermining means 134, whether the maximum undershooting amountN_(USMAX) is equal to, or less than, the allowable undershooting amountN_(UDS). If the determination in either step SG2 or step SG3 is NO, theroutine ends. That is, if the maximum undershooting amount N_(USMAX) isbetween the target undershooting amount N_(USU), which is the upperlimit of the maximum undershooting amount N_(USMAX), and the allowableundershooting amount N_(USD), which is the lower limit of the maximumundershooting amount N_(USMAX), there is no need to execute the learningcorrection routine so the routine ends. If the determination in step SG2is YES, the new learning correction value L_(NEW) (L_(NCUT) or L_(NCAN))to be added to the current time until the start of sweep control t_(C0C)(t_(C0C0T) or t_(C0CAN)) of the clutch C0 in order to avoid the neutraltendency is obtained in steps SN1 to SN6 in FIG. 12, which correspond tostep SG4 in FIG. 11. If the determination in step SG3 is YES, the newlearning correction value L_(NEW) (L_(TU) or L_(TT)) to be added to thecurrent time until the start of sweep control t_(C0C) (t_(C0T)) of theclutch C0 in order to avoid tie-up is obtained in steps ST1 to ST3 inFIG. 13, which correspond to step SG5 in FIG. 11.

In step SN1, which corresponds to the fuel cut state determining means128, it is determined whether a command to cut off the fuel supply tothe engine 10 which is output to the fuel cut apparatus 118 by the fuelcut controlling means 126 during the downshift control operation whilethe vehicle is decelerating has been cancelled. In step SN2, whichcorresponds to the learning number determining means 142, it isdetermined whether the learning number n of the learning correctionroutine for the time until the start of sweep control stored in theEEPROM is exceeding the predetermined number n_(C), for example, 2 to 5.Then, in steps SN3 to SN6, which correspond to the learning correctionvalue calculating means 146, the learning correction value for avoidingthe neutral tendency according to the results of steps SN1 and SN2 iscalculated. That is, if the determination in step SN1 is NO and thedetermination in step SN2 is YES, the normal learning gain G_(F) is madethe gain in step SN3 for the normal learning routine. Then in step SN6,a new learning correction value L_(NCUT) (=L_(C)+G_(F)×N_(USMAX)) iscalculated by adding the product of the normal learning gain G_(F) andthe maximum undershooting amount N_(USMAX) to the current learningcorrection value L_(C).

Further, if the determinations in both steps SN1 and SN2 are NO, becausethe dispersion in the maximum undershooting amount N_(USMAX) due todeviation among vehicles from the learning number n being low isunavoidable, the high speed learning gain G_(K), which is a value largerthan the normal learning gain G_(F), is made the gain in step SN4 sothat the learning correction value L is quickly reflected in the nextshift control operation, and in step SN6, the product of the high speedgain G_(K) and the maximum undershooting amount N_(USMAX) is added tothe current learning correction value L_(C) to obtain the new learningcorrection value L_(NCUT) (=L_(C)+G_(K)×N_(USMAX)). Also, if thedetermination in step SN1 is YES, because the fuel cut is cancelled dueto the fact that the undershooting amount N_(EUS) of the engine 10 islarge, as well as in order to improve fuel efficiency and the like, anundershooting amount N_(US) (N_(EUS)) which does not cancel the fuel cutis necessary in the fewest number of times possible. Therefore, in stepSN5, the new learning correction value L_(NCAN) (L_(NCAN)=L_(C)+L_(NE))is obtained by adding the learning correction value for emergencyneutral avoidance learning L_(NE) to the current learning correctionvalue L_(C). The value of the maximum undershooting amount N_(USMAX)derived from the undershooting amount N_(US) will not be the correctmaximum value because the fuel cut has been cancelled and the enginespeed N_(E) has increased. Therefore, a predetermined value, not theproduct of the maximum undershooting amount N_(USMAX) and the gain Gused during normal learning and the like, is used as the value of thelearning correction value for emergency neutral avoidance learningL_(NE).

In step ST1, which corresponds to the undershooting amount determiningmeans 134, it is determined whether the maximum undershooting amountN_(USMAX) is equal to, or less than, the zero determination value. Ifthe determination in step ST1 is NO, the undershooting amount N_(US) orN_(EUS) of the turbine rotational speed N_(T) or the engine speed N_(E)is generated to some extent, but the state of the automatic transmission14 is close to tie-up so the new learning correction value L_(TU)(=L_(C)−L_(TF)) is obtained by subtracting the learning correction valuefor normal learning L_(TF) from the current learning correction valueL_(C) so as to shorten the current time until the start of sweep controlt_(C0C) (t_(C0T)) of the clutch C0. If the determination in step SN1 isYES, the automatic transmission 14 is in the tie-up state so the newlearning correction value L_(TT) (=L_(C)−L_(TE)) is obtained bysubtracting the learning correction value for emergency tie-up avoidancelearning L_(TE) from the current learning correction value L_(C) so thatthe current time until the start of sweep control t_(C0C) (t_(C0T))becomes shorter than that for normal learning with one execution of thelearning correction routine in order to quickly avoid shift shock. Apredetermined value is used for the learning correction value for normallearning L_(TF) or the learning correction value for emergency tie-upavoidance learning L_(TE).

When the new learning correction value L_(NEW) (L_(NCUT), L_(NCAN),L_(TU) or L_(TT)) is obtained in step SG4 (i.e., steps SN1 to SN6) orstep SG5 (i.e., steps ST1 to ST3), the learning number n is updated instep SG6, which corresponds to the learning number updating means 140,by adding 1 to the last learning number n stored in the EEPROM, and thatvalue is stored in the EEPROM.

Next, in step SG7, which corresponds to the sweep start time calculatingmeans 148, the next time until the start of sweep control t_(C0NEXT)(t_(C0NG), t_(C0NE) or t_(C0NT),=t_(C0C)+L_(NEW)) of the apply pressureP_(C0) of the clutch C0 is calculated by adding the new learningcorrection value L_(NEW) (L_(NCUT), L_(NCAN), L_(TU) or L_(TT)) obtainedby the learning correction value calculating means 146 to the currenttime until the start of sweep control t_(C0C) (t_(C0CUT), t_(C0CAN) ort_(C0T)). The new learning correction value L_(NEW) is calculated instep SG4 (i.e., steps SN1 to SN6) or step SG5 (i.e., steps ST1 to ST3)such that L_(NCAN)>L_(NCUT)>0 in order to increase the current timeuntil the start of sweep control t_(C0C) when there is a neutraltendency, and such that L_(TT)<L_(TU)<0 in order to reduce the currenttime until the start of sweep control t_(C0C) when there is a tie-uptendency.

FIG. 14 is a time chart illustrating a case in which the normal learningroutine or the high speed learning routine for the neutral tendency isexecuted in the shift control operation of the automatic transmission 14during a downshift while the vehicle is decelerating, according to theexemplary embodiment. In the drawing, the solid lines denote valuesbefore execution of the learning routine and the broken lines denotevalues after execution of the learning routine. As illustrated in thedrawing, after execution of the learning routine, the time until thestart of sweep control is increased from t_(C0CUT) (the current timeuntil the start of sweep control t_(C0C)) to t_(C0NG) (the next timeuntil the start of sweep control t_(C0NEXT) of the apply pressure P_(C0)of the clutch C0). As a result, an undershoot U from insufficient applypressure P_(C0) by the clutch C0, which is the hydraulic friction deviceto be released, is reduced. Therefore, shift shock (a phenomenonresembling momentary engine brake) when the engine speed N_(E) increasesdue to application of the brake B1 is reduced. Also, the increase in theturbine rotational speed N_(T) is started earlier (inertia start, timet_(1NG)), and as a result, the shift control (hydraulic pressurecontrol) ends sooner, at time t_(3NG) instead of time t_(3N). This issubstantially the same amount of time as the time from the inertia startuntil the end of the hydraulic pressure control, so if the inertia startis moved back (i.e., started earlier), the hydraulic pressure controlwill end earlier. Also, the only difference in the expression forobtaining the new learning correction value L_(NCUT)(=L_(C)+G×N_(USMAX)) for the normal learning routine and the high speedlearning routine is that the gain G is made either the normal learninggain G_(F) or the high speed learning gain G_(K) depending on thelearning number n. Therefore, except for the fact that the differencebetween the time until the start of sweep control after learning and thetime until the start of sweep control before learning (i.e.,t_(C0NG)−t_(C0CUT)) is greater with the high speed learning routine, thenormal learning routine and the high speed learning routine are thesame.

FIG. 15 is a time chart illustrating a case in which the emergencylearning routine for the neutral tendency is executed in the shiftcontrol operation of the automatic transmission 14 during a downshiftwhile the vehicle is decelerating, according to the exemplaryembodiment. In the drawing, the solid lines denote values beforeexecution of the learning routine and the broken lines denote valuesafter execution of the learning routine. From the drawings, it isevident that the only substantial difference between the cases shown inFIG. 14 and FIG. 15 is that, before execution of the learning routine,the engine speed N_(E) drops to the fuel cut cancellation value C_(F) inFIG. 15 because the undershoot U_(K) in FIG. 15 is greater than theundershoot U in FIG. 14, and as a result, the fuel cut is canceled (timet_(CF)). After the learning routine, the time until the start of sweepcontrol is increased from t_(C0CAN) (the current time until the start ofsweep control t_(C0C)) to t_(C0NE) (the next time until the start ofsweep control t_(C0NEXT) of the apply pressure P_(C0) of the clutch C0).As a result, the undershoot U_(K) from insufficient apply pressureP_(C0) by the clutch C0, which is the hydraulic friction device to bereleased, is reduced. Also, the increase in the turbine rotational speedN_(T) is started earlier (inertia start, time t_(1NE)), and as a result,the shift control (i.e., hydraulic pressure control) ends sooner, attime t_(3NE) instead of time t_(3E). Further, fuel efficiency isimproved because the fuel cut is continued.

FIG. 16 is a time chart illustrating a case in which the emergencylearning routine for tie-up is executed in the shift control operationof the automatic transmission 14 during a downshift while the vehicle isdecelerating, according to the exemplary embodiment. In the drawing, thesolid lines denote values before execution of the learning routine andthe broken lines denote values after execution of the learning routine.As can be seen in the drawing, after execution of the learning routine,the time until the start of sweep control is decreased from t_(C0T) (thecurrent time until the start of sweep control t_(C0C)) to t_(C0NT) (thenext time until the start of sweep control t_(C0NEXT) of the applypressure P_(C0) of the clutch C0). As a result, the apply pressureP_(C0) of the clutch C0, which is the hydraulic friction device to bereleased, decreases sooner, thus reducing the degree of overlap betweenthe application of the clutch C0 and the application of the brake B1. Asa result, shift shock due to lockup, i.e., tie-up, of the automatictransmission 14 is reduced. Further, the increase in the turbinerotational speed N_(T) is started earlier (inertia start, time t_(INT)),and as a result, the shift control (i.e., hydraulic pressure control)ends sooner, at time t_(3NT) instead of time t_(3T). Also, the normallearning routine and the emergency learning routine are substantiallythe same except for i) the fact that the difference between the timeuntil the start of sweep control before learning and the time until thestart of sweep control after learning (i.e., t_(C0T)−t_(C0NT)), whichdiffers depending on whether, in the expression for obtaining the newlearning correction value L_(NEW) (=L_(TU), L_(TT)), the new learningcorrection value L_(TU) (=L_(C)−L_(TF)) derived by subtracting thelearning correction value for normal learning L_(TF) from the currentlearning correction value L_(C), or the new learning correction valueL_(TT) (=L_(C)−L_(TE)) derived by subtracting the learning correctionvalue for emergency tie-up avoidance learning L_(TE) from the currentlearning correction value L_(C) is calculated, is larger with theemergency learning routine, and ii) the fact that, with the normallearning routine, the automatic transmission 14 is close to being in atie-up state such that an undershoot is generated.

Accordingly, in the exemplary embodiment, the learning controlling means144 (step S10) corrects, through learning control, the apply pressure ofat least one of the hydraulic friction devices operated for theclutch-to-clutch downshift so as to increase the amount of drop (i.e.,the undershooting amount N_(US)) in the rotational speed N_(IN) of theinput shaft when the degree of overlap between the release of thehydraulic friction device to be released (i.e., the clutch C0) and theapplication of the hydraulic friction device to be applied (i.e., thebrake B1) is large and the amount of drop (i.e., the maximumundershooting amount N_(USMAX)) in the rotational speed N_(IN) of theinput shaft (i.e., the turbine rotational speed N_(T)) of the automatictransmission 14 is less than the predetermined value (i.e., theallowable undershooting amount N_(USD)) during a clutch-to-clutchdownshift while decelerating. As a result, shift shock due to a largedegree of overlap between the release of the hydraulic friction deviceto be released and the application of the hydraulic friction device tobe applied during a clutch-to-clutch downshift while decelerating isappropriately reduced or eliminated.

Also according to the exemplary embodiment, when a command for theclutch-to-clutch downshift is output, the shift hydraulic pressurecontrolling means 124 maintains the apply pressure P_(C0) of thehydraulic friction device to be released (i.e., the clutch C0) for thepredetermined holding time t_(C0W) at the predetermined holding pressureP_(C0W) which is set lower than the base pressure of the apply pressureP_(C0) and higher than the pressure at which the hydraulic frictiondevice to be released starts to release. The shift hydraulic pressurecontrolling means 124 then smoothly decreases the apply pressure P_(C0)of the hydraulic friction device to be released (i.e., the clutch C0) ata constant rate, while increasing the apply pressure P_(B1) of thehydraulic friction device to be applied (i.e., the brake B1) so that therotational speed N_(IN) of the input shaft (i.e., the turbine rotationalspeed N_(T)) smoothly increases at a constant rate. As a result, theclutch-to-clutch downshift is able to be appropriately executed.

Also according to the exemplary embodiment, when the amount of drop(i.e., the maximum undershooting amount N_(USMAX)) in the rotationalspeed N_(IN) of the input shaft (i.e., the turbine rotational speedN_(T)) is less than the predetermined value (i.e., the allowableundershooting amount N_(USD)), the learning controlling means 144 (stepS10) corrects the holding time t_(C0W) of the holding pressure (i.e.,the current time until the start of sweep control t_(C0C)) of thehydraulic friction device to be released (i.e., the clutch C0) throughlearning so that it becomes shorter. As a result, the amount of dropN_(US) in the rotational speed N_(IN) of the input shaft is increased.

Also according to the exemplary embodiment, when the amount of drop(i.e., the maximum undershooting amount N_(USMAX)) in the rotationalspeed N_(IN) of the input shaft (i.e., the turbine rotational speedN_(T)) of the automatic transmission 14 is less than the predeterminedvalue (i.e., the allowable undershooting amount N_(USD)), the learningcontrolling means 144 (step S10) corrects, so as to advance, the time atwhich to start decreasing pressure t_(C0NEXT)(t_(C0NT),=t_(C0C)+L_(NEW)) from the holding pressure P_(C0W) of thehydraulic friction device to be released in the next clutch-to-clutchdownshift through learning by adding (actually, subtracting, by makingL_(TU) or L_(TT) a negative number) the learning correction valueL_(NEW) (L_(TU) or L_(TT)) to the time at which to start decreasingpressure (i.e., the current time until the start of sweep controlt_(C0C) (t_(C0T))) from the holding pressure P_(C0W) of the hydraulicfriction device to be released (i.e., the clutch C0) during in the lastclutch-to-clutch downshift. As a result, the amount of drop N_(US) inthe rotational speed N_(IN) of the input shaft increases.

Also according to the exemplary embodiment, when the amount of drop(i.e., the maximum undershooting amount N_(USMAX)) in the rotationalspeed N_(IN) of the input shaft (i.e., the turbine rotational speedN_(T)) of the automatic transmission 14 is less than the predeterminedvalue (i.e., the allowable undershooting amount N_(USD)), the learningcontrolling means 144 (step S10) corrects the holding time of theholding pressure (i.e., the current time until the start of sweepcontrol t_(C0C) (t_(C0T))) of the hydraulic friction device to bereleased through learning to be shorter when the amount of drop (i.e.,the maximum undershooting amount N_(USMAX)) is equal to, or less than,the zero determination value for determining that the amount of dropN_(USMAX) is a small value such as zero or therearound than when theamount of drop (i.e., the maximum undershooting amount N_(USMAX)) is notequal to, or less than, the zero determination value, by using a largerlearning correction value L_(TT). As a result, the amount of increase inthe amount of drop N_(US) with one execution of learning control islarger so the amount of drop N_(US) in the rotational speed N_(IN) ofthe input shaft is quickly increased.

Although the invention has been described in detail in terms ofexemplary embodiments with reference to the drawings, the invention isnot limited to those exemplary embodiments.

For example, in the foregoing exemplary embodiment, the clutch-to-clutchdownshift operation of the automatic transmission 14 during decelerationof the vehicle is performed with a 3→2 downshift. Alternatively,however, the operation may also be performed with a 5→4, 4→3, 2→1 orother downshift.

Also, in the exemplary embodiment, the automatic transmission 14 is a FFtransverse-mounted transmission with five forward speeds which isconstructed of a combination of three planetary gearsets 40, 42, and 46.Alternatively, however, the number of planetary gearsets which incombination make up the automatic transmission 14 may be a number otherthan three. The automatic transmission 14 may also be alongitudinal-mounted transmission for a FR (front engine, rear drive)vehicle, or the like.

Also in the exemplary embodiment, the learning control means 144corrects the time at which to start decreasing pressure (i.e., thecurrent time until the start of sweep control t_(C0C) (t_(C0T))) fromthe predetermined apply pressure P_(C0W) of the clutch C0, which is thehydraulic friction device to be released, through learning so that it isadvanced, and increases the undershoot amount N_(US) so as to avoid thetie-up tendency. Alternatively, however, the tie-up tendency can also beavoided by correcting the predetermined apply pressure P_(C0W) throughlearning so that it decreases, thus advancing the time at which theclutch C0 is released and increasing the undershoot amount N_(US). Also,the tie-up tendency can also be avoided by increasing the undershootamount N_(US) by applying the brake B1 later by having the learningcontrolling means 144 correct, through learning, the time at which tostart increasing pressure (i.e., the time during which the applypressure P_(B1W) is maintained after the start of the shift) from thepredetermined apply pressure P_(B1W) that is set lower than the pressureat which the apply pressure P_(PB1) of the brake B1, which is thehydraulic friction device to be applied, starts to be applied, so as todelay that time at which to start increasing pressure (i.e., increasethe time during which the apply pressure P_(B1W) is maintained after thestart of the shift), or correct the predetermined apply pressure P_(B1W)so as to make it smaller.

While the invention has been described with reference to exemplaryembodiments thereof, it is to be understood that the invention is notlimited to the exemplary embodiments or constructions. To the contrary,the invention is intended to cover various modifications and equivalentarrangements. In addition, while the various elements of the exemplaryembodiments are shown in various combinations and configurations, whichare exemplary, other combinations and configurations, including more,less or only a single element, are also within the spirit and scope ofthe invention.

1. A shift control apparatus for a vehicular automatic transmission,comprising: a fuel cut apparatus which performs a fuel cut in which asupply of fuel to an engine is cut off when an engine speed exceeds apredetermined value during deceleration of a vehicle; an automatictransmission in which a gearshift is achieved with a clutch-to-clutchdownshift in which a hydraulic friction device to be released isreleased and a hydraulic friction device to be applied is applied; and acontroller which corrects, through learning control, an apply pressureof at least one of the hydraulic friction devices to be operated for theclutch-to-clutch downshift such that an amount of drop in a rotationalspeed of an input shaft of the automatic transmission increases whenthat amount of drop is less than a predetermined value during theclutch-to-clutch downshift.
 2. The shift control apparatus for avehicular automatic transmission according to claim 1, wherein, when acommand for the clutch-to-clutch downshift is output, the controllermaintains the apply pressure of the hydraulic friction device to bereleased for a predetermined holding time at a predetermined holdingpressure which is set lower than a base pressure of the apply pressureand higher than a pressure at which the hydraulic friction device to bereleased starts to release, and then smoothly decreases the applypressure of the hydraulic friction device to be released at a constantrate, while increasing the apply pressure of the hydraulic frictiondevice to be applied so that the rotational speed of the input shaftsmoothly increases at a constant rate.
 3. The shift control apparatusfor a vehicular automatic transmission according to claim 2, wherein thecontroller corrects, through learning, the holding time of the holdingpressure of the hydraulic friction device to be released so as todecrease when the amount of drop in the rotational speed of the inputshaft is less than the predetermined value.
 4. The shift controlapparatus for a vehicular automatic transmission according to claim 3,wherein, when the amount of drop in the rotational speed of the inputshaft is less than the predetermined value, the controller obtains atime at which to start decreasing pressure from the holding pressure ofthe hydraulic friction device to be released in the nextclutch-to-clutch downshift by subtracting a learning correction valuefrom the time at which to start decreasing pressure from the holdingpressure of the hydraulic friction device to be released in the lastclutch-to-clutch downshift.
 5. The shift control apparatus for avehicular automatic transmission according to claim 3, wherein, when ithas been determined that the amount of drop in the rotational speed inthe input shaft of the automatic transmission is less than thepredetermined value, the controller corrects the holding time of theholding pressure of the hydraulic friction device to be released throughlearning so as to be shorter when it has been determined that the amountof drop is equal to, or less than, a zero determination value than whenit has been determined that the amount of drop is not equal to, or lessthan, the zero determination value by using a larger learning correctionvalue.
 6. The shift control apparatus for a vehicular automatictransmission according to claim 2, wherein, when it has been determinedthat the amount of drop in the rotational speed in the input shaft ofthe automatic transmission is less than the predetermined value, thecontroller corrects the holding time of the holding pressure of thehydraulic friction device to be released through learning so as to beshorter when it has been determined that the amount of drop is equal to,or less than, than a zero determination value than when it has beendetermined that the amount of drop is not equal to, or less than, thezero determination value, by using a larger learning correction value.7. A shift control method for a vehicular automatic transmissionprovided with a fuel cut apparatus which performs a fuel cut in which asupply of fuel to an engine is cut off when an engine speed exceeds apredetermined value during deceleration of a vehicle, and an automatictransmission in which a gearshift is achieved with a clutch-to-clutchdownshift in which a hydraulic friction device to be released isreleased and a hydraulic friction device to be applied is applied, theshift control method comprising the step of: correcting, throughlearning control, an apply pressure of at least one of the hydraulicfriction devices to be operated for the clutch-to-clutch downshift suchthat an amount of drop in a rotational speed of an input shaft of theautomatic transmission increases when that amount of drop is less than apredetermined value during the clutch-to-clutch downshift.
 8. The shiftcontrol method for a vehicular automatic transmission according to claim7, further comprising the step of: when a command for theclutch-to-clutch downshift is output, maintaining the apply pressure ofthe hydraulic friction device to be released for a predetermined holdingtime at a predetermined holding pressure which is set lower than a basepressure of the apply pressure and higher than a pressure at which thehydraulic friction device to be released starts to release, and thensmoothly decreasing the apply pressure of the hydraulic friction deviceto be released at a constant rate, while increasing the apply pressureof the hydraulic friction device to be applied so that the rotationalspeed of the input shaft smoothly increases at a constant rate.
 9. Theshift control method for a vehicular automatic transmission according toclaim 8, wherein, the holding time of the holding pressure of thehydraulic friction device to be released is corrected through learningso as to increase when the amount of drop in the rotational speed of theinput shaft is less than the predetermined value.
 10. The shift controlmethod for a vehicular automatic transmission according to claim 9,wherein, when the amount of drop in the rotational speed of the inputshaft of the automatic transmission is less than the predeterminedvalue, a time at which to start decreasing pressure from the holdingpressure of the hydraulic friction device to be released in the nextclutch-to-clutch downshift is obtained by subtracting a learningcorrection value from the time at which to start decreasing pressurefrom the holding pressure of the hydraulic friction device to bereleased in the last clutch-to-clutch downshift.
 11. The shift controlmethod for a vehicular automatic transmission according to claim 9,wherein, when it has been determined that the amount of drop in therotational speed in the input shaft of the automatic transmission isless than the predetermined value, the holding time of the holdingpressure of the hydraulic friction device to be released is correctedthrough learning so as to be shorter when it has been determined thatthe amount of drop is equal to, or less than, than a zero determinationvalue than when it has been determined that the amount of drop is notequal to, or less than, the zero determination value by using a largerlearning correction value.
 12. The shift control method for a vehicularautomatic transmission according to claim 8, wherein, when it has beendetermined that the amount of drop in the rotational speed in the inputshaft of the automatic transmission is less than the predeterminedvalue, the holding time of the holding pressure of the hydraulicfriction device to be released is corrected through learning so as to beshorter when it has been determined that the amount of drop is equal to,or less than, than a zero determination value than when it has beendetermined that the amount of drop is not equal to, or less than, thezero determination value by using a larger learning correction value.